1. Technical Field
The present invention relates to a variable printing machine for printing print images which are different in top-bottom length.
2. Background Art
There has hitherto been proposed a variety of variable printing machines whereby print images different in top-bottom length are printed on a continuous sheet or web of paper so that there may be no extra space between succeeding printed images.
For example, there have been proposed an intermittent feed type variable printing machine (JP 2004-351640 A) and a sleeve exchangeable cylinder type variable printing machine (JP 2009-190402 A).
In an intermittent feed type printing machine, the printing surface is constituted by a circumferential portion of the peripheral surface of a printing cylinder. Printing on the continuous web of paper is effected intermittently by repeating a cycle of its forward feed of travel, stop and backward feed of travel. The top-bottom length of a print image is shorter than the peripheral length of the printing cylinder.
In a sleeve exchangeable cylinder type variable printing machine, a printing sleeve is mounted removably on a supporting shaft to constitute a printing cylinder. The printing surface is constituted by the total length of the peripheral surface of the printing cylinder. The printing sleeve is exchanged among ones of different diameters to change the peripheral length of the printing cylinder for printing. The top-bottom length of a print image is identical to the peripheral length of the printing cylinder.
The intermittent feed type variable printing machine, while furnishing printed images of top-bottom lengths that can be set as desired, cannot much raise the speed of their production because of repetitions of forward feed to travel, stop and backward feed to travel of a continuous web of paper, and it is therefore not suited for large-lot production.
It also raises problems such as that an apparatus needed to so feed a continuous web of paper becomes complex and costly, and a control software required to control operations of the apparatus becomes highly costly.
The sleeve exchangeable cylinder type variable printing machine allows a continuous web of paper to be fed to travel at a fixed rate and achieving an enhanced rate of print production, and hence it is suited for large-lot production. And, the apparatus for feeding a continuous paper is simple and inexpensive and so is a software for controlling operations of the apparatus. Because of change in diameter of a printing cylinder, however, there arises a problem that an impression cylinder may not properly be in contact with the printing cylinder, thereby giving rise to incorrect image printing.
In view of problems as mentioned above, it is an object of the present invention to provide a variable printing machine, i.e. a machine for printing images different in top-bottom length by change in diameter of a printing cylinder, in which the printing cylinder and an impression cylinder can be brought into a proper state of contact with each other, thereby achieving correct image printing.